force route for ping probe

Hi guys.
My border router has tree isp peers providers.
There is an active default route and two backups (with lower distance).
I would like to ping some internet ips (root servers for example) using those backup links.
The idea is to compare service latency between my providers.
Is there some way to force ping to go over those inactive routes ?
I already tryed with src-address and interface paramenter , but it does not work.

ping 198.41.0.4 interface=vlan418_ITX src-address=170.94.1X6.78

Im thinking about some routing policy, but im afraid I can add extra cpu load just for a ping test since my device is routing 8Gbps.
btw:
Im using smokeping with OpenSSHMikrotikRouterOSPing plugin.
Any idea would be wellcome.
Leandro.

You can have other independent routing tables:

/ip route
add dst-address=0.0.0.0/0 gateway=<ISP1 gateway> routing-mark=ISP1
add dst-address=0.0.0.0/0 gateway=<ISP2 gateway> routing-mark=ISP2
...

And then use them with ping:

/ping 198.41.0.4 routing-table=ISP2

Wow … seems very nice solution.
I will try it , so you can specify wich table to use and only will be used with that ping … no cpu overload.
Thanks.

It worked !!!
Thanks.